Trendy plus-size fashions were so hard to find several years ago that Nina Williams would wear maternity clothes. But during a recent shopping trip to the new Torrid store at 7 N. State St., the 26-year-old teacher said that has changed.

"Everything I want I can get from a plus-size store now," Williams, who lives in South Shore, said after buying a faux leather jacket from the store that she had been seeking online.

Torrid's Loop flagship, which opened two weeks ago, is one of 60 new stores the plus-size brand is launching across the country this year as it seizes on strong demand for stylish plus-size apparel.

The brand, which sells on-trend jeans, dresses, bathing suits, underwear and more for sizes 12 through 28, at prices of about $50 to $70, will have 350 stores by the end of the year catering to "young, voluptuous women," the company said.

Sales at plus-size women's clothing stores grew at an average annual rate of 3.2 percent since 2009, to $9.4 billion last year, and that growth rate is expected to accelerate to 5.8 percent annually through 2019, pushed by climbing disposable income and obesity rates, according to market research firm IBISWorld. That figure doesn't include mass merchants such as Target and Wal-Mart.

Market research firm NPD Group, which does include the retail giants in its calculations, put women's plus-size apparel revenue in the U.S. at $17.6 billion last year, a slight dip from the year before but up 8 percent from 2012. It accounts for about 15 percent of the overall women's apparel market.

The fashion industry's notorious neglect of plus-size shoppers has long mismatched the oft-cited fact that the average American woman wears a size 14. That statistic comes from a 2004 study sponsored by the U.S. military and several clothing companies. While the benchmark is still useful, it has lost some meaning as Americans have been trending heavier and many clothing manufacturers in turn have revamped their sizing standards. What was once a 12 is now a 10, said Jack Plunkett, CEO of market research firm Plunkett Research.

A shift in recent years has seen more designer collaborations and high-end labels offering plus sizes, as well as more general retailers, such as H&M and Forever 21, expanding lines to include plus-size apparel, IBISWorld said.

While the biggest player in the space is Ascena Group, owner of Lane Bryant, newer specialty brands such as Eloqqui, an online fast-fashion brand originally launched in 2011 as an arm of The Limited but then relaunched last year as a separate company, and Torrid aim at a younger customer.

Torrid, which debuted in 2001, is owned by California-based Hot Topic, which was taken private in 2012 for $600 million by private equity firm Sycamore Partners. Though financial information isn't publicly available, IBISWorld expected Torrid to generate $190 million last year.

Williams, pointing to a leopard-print bikini in the Torrid window, said the styles from the new batch of plus-size brands flatter bodies rather than try to hide them. The new store is on her way home from work — an exciting, if financially perilous, addition to her commute.